1. Field of the Invention
The present invention relates to multi-room air conditioning apparatuses and, more particularly, relates to an initialization procedure for an electronic expansion valve that serves as a decompression device for the multi-room air conditioning apparatuses.
2. Description of the Related Art
A refrigerant circuit configuration of a typical multi-room air conditioning apparatus includes a plurality of indoor units and an outdoor unit having a compressor, an outdoor heat exchanger, and a four-way valve for switching a refrigerant flow direction. Also, each indoor unit has an electronic expansion valve for decompressing a condensed refrigerant. The electronic expansion valve is disposed in the outdoor unit, the indoor unit, or a branch box. The compressor, the four-way valve, and the electronic expansion valve are connected to and controlled by a control device, depending on various operating conditions.
In response to an operation command issued by any of the indoor units in the rooms all of which are in a shutdown state, the compressor starts up and delivers a refrigerant, which goes through the four-way valve to the outdoor heat exchanger where, in a cooling mode, the refrigerant is condensed. Then, the refrigerant is decompressed through an electronic expansion valve and is subjected to heat exchange using evaporation action in the indoor unit, and is finally returned to the compressor. In a heating mode, a refrigerant flow is turned by the four-way valve to the opposite direction of that in the cooling mode. Then the refrigerant is condensed at the indoor unit, is decompressed through the electronic expansion valve, and then goes to the outdoor unit where the refrigerant is subjected to heat exchange using evaporation action in the outdoor heat exchanger and is finally returned to the compressor.
The electronic expansion valve can adjust the decompression degree and the amount of refrigerant circulation by changing the valve opening degree. The electronic expansion valve corresponding to the indoor unit which has issued the operation command is controlled with regard to the valve opening degree by monitoring the rotational speed of the compressor, discharge temperatures, the degree of supercooling, and the like so as to provide a proper refrigerating cycle. Other electronic expansion valves corresponding to indoor units which have issued no operation command are also controlled not to full close but to slight opening degree so as to prevent valve sticking or refrigerant pooling.
As described above, in order to provide valve opening degree control for the electronic expansion valve, the opening degrees of all of the electronic expansion valves are all closed so as to adjust the zero (starting) point before the refrigeration cycle is activated. This operation is referred to the initialization of the electronic expansion valve.
A specific initialization control operation is described below. Assuming that the electronic expansion valve that has not yet been initialized had a full open opening degree A, the control device issues a command for closing the electronic expansion valve by the amount of −A or more. This operation inevitably results in adjusting zero point, regardless of any opening degree before the initialization. This operation takes a few seconds for each electronic expansion valve.
When the initialization of the electronic expansion valves does not complete, the procedure for activating the refrigerating cycle is as follows: First, all of the electronic expansion valves are initialized. Then, immediately after activation of the compressor following the completion of the expansion valve initialization, the electronic expansion valves is operated and set to a predetermined opening degree.
However, the more the number of the indoor units to be connected to the entire system increase, the more the number of the corresponding electronic expansion valves increase. As described above, the completion of the initialization of all the electronic expansion valves followed by the activation of the compressor results in a significant loss of time from the issuance of an operation command until the activation of the refrigerating cycle.
The relationship between the refrigerating cycle operation and the electronic expansion valve initialization of conventional multi-room air conditioning apparatuses is disclosed in Patent Literature 1 and Patent Literature 2.
Patent Literature 1 discloses a multi-room air conditioning apparatus employing an electronic expansion valve that allows a certain amount of a refrigerant to flow even at the fully closed opening degree for the purpose of fully closing the electronic expansion valves for initialization without suspending the compressor during the system operation.
Patent Literature 2 discloses a multi-room air conditioning apparatus in which a plurality of electronic expansion valves are arranged so as to correspond to one indoor unit, one of which is initialized in advance to provide a predetermined opening after the initialization and subsequently the remaining electronic expansion valves are preformed the same operation in order, for the purpose of fully closing the electronic expansion valves for initialization without suspending the compressor during the system operation.